Hard metal plate for rock drill and rock drill

ABSTRACT

In a hard metal plate for insertion in to a seat formed at one end of a drill shaft of a rock drill, comprising a substantially rectangular base shape having two opposed long sides extending in the axial direction of the drill shaft which are at least partially covered by the seat, two opposed, substantially axial free short sides, a radial bottom side facing towards the seat and a cutting face facing away from the seat, both short sides are formed by an axial section having a purely axial direction component and a conical section inclined towards the axial direction, so that at the short side, the substantially rectangular plate tapers towards the bottom side.

The invention relates to a hard metal plate for insertion in to a seatformed at one end of a drill shaft of a rock drill. The generic hardmetal plate should comprise a substantially rectangular base having twoopposed, in particular parallel long sides extending in the axialdirection of the drill shaft. In the inserted state of the hard metalplate, the long sides are at least partially covered by the seat of thedrill shaft. The long sides are configured to be flat. Furthermore, therectangular basic shape is defined by two opposed, substantially axialfree short sides, a bottom side facing towards the seat and a cuttingface facing away from the seat.

Such hard metal plates have proved successful in practice since they areeasy to manufacture and mount on the drill shaft. Such a hard metalplate is known, for example, from U.S. Pat. No. 3,089,552. The knownhard metal plate is inserted in a slot at the end of the drill shaft. Ina side view, the hard metal plate is provided with a roof-shaped cuttingface with flattened tip. The cutting edges lie on the longitudinaltransition edge between the cutting face and the long side, whichprecedes the longitudinal transition edge in the direction of rotation.The cutting edges are connected to one another by means of a centralcutting edge in the flattened tip region. The known hard metal plateextends radially over the drill head of the drill shaft which receivesthe hard metal plate.

A further development of the known hard metal plate is given in EP 0 836919 B1. According to this, both roof flanks of the cutting face of thehard metal plate are provided with stepped sections which run radiallyoutwards from a projecting tip in an axially resetting manner. As aresult of the stepped sections, a plurality of jagged initial cuts areformed. With this measure for increasing the drilling efficiency bymeans of producing a plurality of cutting edges at the cutting face, thedisadvantage emerged that the life of such hard metal plates issignificantly reduced.

It is the object of the invention to overcome the disadvantages of theprior art, in particular to optimise a hard metal plate for a rock drillhaving a substantially rectangular basic shape in particular having aroof-shaped cutting face in such a manner that the life of the hardmetal plate is increased whilst ensuring a high drilling efficiency.

According to a first aspect of the invention, the two short sides areformed by an axial section having a purely axial direction component anda conical section inclined towards the axial direction, so that at theshort side, the substantially rectangular plate tapers towards thebottom side. At this point, it may be noted that the pure axial sectionpreferably opens axially linearly, i.e. free from bends, into thecutting face in a smooth angular manner in order to strength the hardmetal plate at the cutting face with a maximum of hard metal material.

A particularly high drilling efficiency was established with thisconicity at the bottom side of the hard metal plate. It was shown thatthe conicity at the bottom side favourably influences the removal ofdrilling dust. Despite the putative weakening at the bottom side, thelives of the hard metal plate are sufficiently high. The hard metalplate is strengthened in the area of the front face as a result of theunchanged axial section. It was surprisingly shown that the conicity ofa bottom side increased the drilling efficiency of the hard metal plateinsofar as a significant reduction in the drilling heat generated whencutting with the hard metal plate is achieved. This reduction in theheat generation was clearly the result of reduced friction between thematerial to be drilled and the hard metal plate because with theconicity, a substantially smaller part of the outer side of the hardmetal plate is brought into engagement with the material to be drilled.

In a preferred embodiment, the conical section is inclined with respectto the axial direction by less than 10°, preferably by about 6°, whereinthe angle of inclination of the axial section is approximately zerountil this opens in to the cutting face. In this way, the hard metalplate is not centro-symmetric with regard to the conicity on the bottomside. With these inclinations, an optimum compromise was achievedbetween the life and efficient removal of drilling dust. The conicalsection preferably forms more than half, preferably a third of the axiallength of the short side. The longer the conical section, the more anyblockage in the area of the cutting face is avoided during drilling.Alternatively, the axial section can form more than half, preferably athird of the axial length of the short side, thus increasing thestrength of the hard metal plate. In a further development of theinvention, the conical section and the axial section are convexly curvedand in particular are separated from one another by a form kink. In thisway, the strength of the hard metal plate is increased.

In a preferred embodiment of the invention, the conical section isfaceted towards the long side in order to thereby further reduce thefriction between the hard metal plate and the material to be drilled.

Particularly good removal properties were then achieved if the conicalsection runs linearly in the axial direction from the axial sectiontowards the bottom side.

According to a second aspect of the invention, a concave grooveextending linearly in the axial direction is preferably formed on atleast one long side, preferably in each case on both long sides. Theaxially extending linear groove defines a locally fixed removal channelfor drilling dust from the cutting face. It was surprisingly found thatvery good removal properties are obtained by the purely axial lineargroove guide. A helical groove guide extending in the coil of the drillshaft is not necessary for this purpose. As a result of the linearity ofthe removal groove, the hard metal plate according to the invention withimproved drilling dust removal properties can be produced very simplyand cost-effectively.

The groove preferably extends directly away from the cutting face andthe groove opens along the linear axial profile into the bottom side. Asa result of the conical section according to the first aspect of theinvention, the groove can be reduced in the axial direction.

Particularly good properties with regard to removal of drilling dustwhilst ensuring an indicated seat of the hard metal plate on the drillshaft were achieved if the groove is formed on the long side at atransition between the long side and adjacent short side.

A further aspect of the invention relates to the cutting face whichshould comprise two long cutting edges. The cutting edges meet in a tipregion and each comprise an edge section close to the tip region and anedge section remote from the tip region. Both edge sections are inclinedtowards a radial direction perpendicular to the axial direction.According to the invention, the edge section close to the tip region ismore strongly inclined than the edge section remote from the tip regionwherein a transition region between the edge section close to the tipregion and the edge section remote from the tip region is continuouslyconcavely curved.

As a result of the different inclinations of the two long cutting edgesections at the cutting face, a significant increase in the drillingefficiency is achieved. In addition, with the continuously curvedtransition between the two differently inclined cutting edge sections,the life of the hard metal plate is not adversely affected or barelyadversely affected despite the increase in the drilling efficiency.

In a preferred embodiment of the invention, the long cutting edges eachconsist of a linear edge section close to the tip region and a linearedge section remote from the tip region.

In a further development, the edge section remote from the tip region isinclined with respect to the associated radial direction by about 5° to20°, preferably by about 12° or 13°. Furthermore, the edge section closeto the tip region is more than twice as steeply inclined with respect tothe associated radial direction by about 25° to 35°, preferably by about29°.

Optimisation of the drilling efficiency is achieved if the linear edgesection remote from the tip region is many times longer than the linearedge section close to the tip region, preferably five times, seven timesor ten times as long.

Furthermore, the cutting face can comprise two short cutting edges whichextend substantially linearly from the respective long side of the hardmetal plate into the tip region with the same inclination towards theradial direction. In this case, the short cutting edges can be inclinedwith respect to the associated radial direction by about 25° to 35°,preferably about 31° or 32°.

In a further development of the invention, the long cutting edgesseparate two mutually inclined front flanks which are delimited by anadjacent short cutting edge and are inclined according to the relevantlong cutting edge and short cutting edge.

The course of the long and/or short cutting edges at the cutting face ispreferably point-symmetrical to the tip region which is crossed by anaxis of rotation of the hard metal plate.

In a further aspect of the invention, the generic hard metal plate isfurther developed in that when considered in an axial projection, twolong cutting edges extending linearly radially outwards from a commontip region, which open in a linear course in the respective short side,are inclined to a flat radial extension of the long sides, which areparallel to one another, at a non-negligible angle greater than 1° andless than 10°. The long cutting edges are preferably inclined to theflat radial extension of the flat sides by 5° or 6°. In this way, thelife and the drilling efficiency of the hard metal plate cansurprisingly be increased.

In a further aspect of the invention, both short sides of the hard metalplate are formed by a substantially flat side section remote from thebottom side and a stepped side section close to the bottom side with atleast two steps which in particular radially set back the hard metalplate towards the bottom side.

It was surprisingly found that an improved drilling dust removalperformance is achieved with a back-setting on the short side section ofthe hard metal plate facing away from the cutting face. In this way, thedrilling efficiency is significantly increased without needing to acceptlosses in regard to the life of the hard metal plate. The hard metalplate preferably tapers in the axial course of the stepped side sectiontowards the bottom side. The longitudinal extension of the hard metalpreferably decreases in the radial direction towards the bottom side.The stepped side section, in particular each step, is defined by aradial jump surface and an axial pedestal surface in the axial course.In this case, the pedestal surface can be larger than the jump surface,in particular is twice as large or three times as large as the jumpsurface.

Particularly good drilling dust removal properties are achieved if thepedestal surface is slightly inclined with respect to the axialdirection, in particular between 1° and 20°.

In a preferred embodiment of the invention, the front side issubstantially pyramid-shaped.

It is clear that the aforesaid aspects of the hard metal plate accordingto the invention can be combined with one another.

The invention further relates to a rock drill having a drill shaft, oneend whereof can be firmly inserted in a drill and the other end whereofcomprises a seat for firmly receiving a hard metal plate according tothe invention. The concave groove of the hard metal plate extendinglinearly in the axial direction is preferably not covered by theretaining flanks of the seat of the drill shaft. The hard metal plate isdimensioned in such a manner that it protrudes radially beyond the drillshaft at least in the area of its cutting face especially at the axialheight of the axial section. A transition between the hard metal plateand the drill shaft at the axial height of the bottom side of the hardmetal plate is preferably continuous in the radial direction, inparticular is free from shoulders.

Further advantages, properties and features of the invention will becomeapparent from the following description of preferred embodiments of theinvention with reference to the appended drawings in which:

FIG. 1 a shows a long side view of a hard metal plate according to theinvention in a first embodiment;

FIG. 1 b shows a short side view of the hard metal plate according toFIG. 1;

FIG. 1 c shows a cutting face view of the hard metal plate according toFIGS. 1 a and 1 b;

FIG. 1 d shows a side view of the rock drill according to the invention;

FIG. 1 e shows a detail view A of the rock drill according to FIG. 1 d;

FIG. 2 a shows a perspective view of a hard metal plate according to theinvention in a second embodiment;

FIG. 2 b shows a long side view of the hard metal plate according toFIG. 2 a;

FIG. 2 c shows a short side view of the hard metal plate according toFIGS. 2 a and 2 b;

FIG. 2 d shows a front face view of the hard metal plate according toFIGS. 2 a to 2 c;

FIG. 2 e shows a side view of the rock drill with the hard metal plateaccording to FIGS. 2 a to 2 d;

FIG. 2 f shows a detail view A according to FIG. 2 e;

FIG. 3 a shows a side view of a rock drill according to the inventionwith a hard metal plate in a third embodiment;

FIG. 3 b shows a detail view A according to FIG. 3 a;

FIG. 4 a shows a side view of a rock drill according to the inventionwith a hard metal plate in a fourth embodiment;

FIG. 4 b shows a detail view A according to FIG. 4 a.

In FIG. 1, the hard metal plate in a first embodiment according to theinvention is generally provided with the reference numeral 1. The hardmetal plate 1 has a substantially rectangular base structure, as can beseen in particular in FIGS. 1 c and 1 b. The substantially rectangularbase structure should be defined by two opposing long sides 3, parallelto one another, having flat side faces and by two opposing short sides 5having slightly concavely curved side faces. A bottom side 7 which isorthogonal both to the short sides 5 and also to the long sides 3, and asubstantially roof-shaped front side 9 in side view are located oppositeto one another and have the same radial surface extension in axialprojection.

The front side 9, when viewed three-dimensionally, has a substantiallypyramidal form with four flat cutting flank sections 11 to 17 which areeach delimited by the long side 3, the short side 5, a main cutting edge19 and a short cutting edge 21.

As shown in FIG. 1 a, the front-side region of the hard metal plate 1 isconfigured as roof-shaped, wherein the main cutting edge 19 has a linearedge section 25 near the short side and a linear shorter edge section 27remote from the short side. The inclination of the edge section 27remote from the short side with respect to a radial direction R issignificantly greater than the inclination of the edge section 25 nearthe short side. The angle of inclination between the edge section 27remote from the short side and the radial direction R is around 29°whereas the angle of inclination of the edge section 25 near the shortside is around 13°.

The transition between the linear edge section 27 remote from the shortside and the edge section 25 near the short side is continuouslyconvexly curved without forming an edge, as shown in FIG. 1 a.

The long cutting edge 19 crosses the short cutting edge 21 in a tipregion 31. The short cutting edge 21 is slightly curved in sections sothat when observing both short cutting edge sections, a slight S shapecan be identified. On the other hand, when viewed in axial projection,the long cutting edge 19 extends from the respective short side 5 to thetip region 31 and continues linearly and slightly offset towards theopposite short side 5.

In the course of the axial direction A from the front side 9, the shortside 5 has an axial section 33 which substantially accounts for onethird of the total axial length of the short side 5. The axial section33 is adjoined by a conical section 37, forming a transition edge 35,which substantially accounts for two thirds of the total axial length ofthe short side 5. The conical section 37 runs substantially linearly inthe axial direction A and forms an angle α of about 6° with respect tothe axial direction A.

The bottom side 7 has two chamfers 41, 43 accounting for a third of thetotal width of the bottom side 7, having an angle of about 45° to thebottom side, which facilitates the insertion of the hard metal plate 1into a slot in a drilling head of a drill shaft 51 (see FIG. 1 d).

FIGS. 1 d and 1 e show the hard metal plate 1 inserted in the slot onthe drilling head 53 of the drill shaft 51.

As can be seen, the hard metal plate 1 goes over continuously into thedrill shaft 51 free from transitions and shoulders. The spiral-shapedhelical groove 55 of the drill shaft 51 runs out linearly on thedrilling head 53. The drilling head 53 comprises two opposingslit-forming flanks 57 having parallel inner faces (not shown in detail)which for the most part cover the long sides 3 of the hard metal plate 1in extensive contact. In the course of the conical section 37 and on theaxial section 33 the hard metal plate 1 protrudes radially beyond theradial dimension of the drill shaft 51.

As can be seen in FIG. 1 c, the long cutting edge 19 extendssubstantially in a radial direction R. However, the main cutting edge 19does not extend parallel to the radial extension of the long side 3 butis slightly inclined thereto. In this way, when viewing a direction ofrotation D, the trailing cutting flank sections 11, 17 are designed tobe stronger than the leading cutting flank sections 13, 15.

FIGS. 2 a to 2 f show another embodiment of the hard metal plate for arock drill according to the invention, wherein for better legibility ofthe description of the figures, the same reference numerals as those ofthe embodiment according to FIGS. 1 a to 1 e, increased by 100, are usedfor identical and similar components of the hard metal plate and rockdrill according to FIGS. 2 a to 2 f.

The hard metal plate 101 shown in FIGS. 2 a to 2 f differs from the hardmetal plate 1 according to FIGS. 1 a to 1 f in that an axial groove 163is formed on the leading edge region 161 of the long side 103 in thedirection of rotation D, which groove extends linearly axially from thefront face 109 to the bottom side 107. The groove 163 is concavelycurved and occupies approximately ⅙ of the width of the long side 103 ofthe hard metal plate 101. In the area of the axial section 133 of theshort side 105, the groove 163 has a constant width which decreases onthe conical section 137 towards the bottom side 107 according to theconicity. A transition between the groove 163 and the conical section137 can be configured as angular, wherein alternatively this transitioncan be configured without a hard edge suitably rounded and continuous inform.

The groove 163 is used to remove drilling dust produced during thecutting of rock, from the cutting zone axially towards the drillingshaft 151, in particular towards the drilling dust groove 155.

As can be seen from FIG. 2 f, the groove 163 opens continuously into thedrilling dust groove 155. Furthermore, it can be seen from FIG. 2 f thatthe slotted flank 157 of the drilling head 157 approximately occupiesthe entire flat side 103, wherein the groove 163 remains unoccupied bythe slotted flank 157 so as to ensure unhindered removal of drillingdust from the axial groove 163 towards the helical groove 155.

FIGS. 3 a and 3 b show another preferred embodiment of the hard metalplate for a rock drill according to the invention, wherein for betterlegibility of the description of the figures, the same referencenumerals as those of the embodiment according to FIGS. 1 a to 1 e, or 2a to 2 f, increased by 200 or 100, are used for identical and similarcomponents of the hard metal plate and rock drill.

The hard metal plate 201 differs from the hard metal plate 101 accordingto FIGS. 2 a to 2 f in that the axial section 233 substantially accountsfor ⅔ of the total length of the short side 205. On the other hand, theconical section 237 accounts for only about ⅓ of the axial length of theshort side 205. As a result of this weaker conicity compared with theembodiment according to FIGS. 2 a to 2 f, a shoulder 269 is formed onthe bottom side 7 which defines a substantially triangular intermediatespace 271 between the drill shaft 251 and the bottom side 207 of thehard metal plate 201.

The jump-like transition between the hard metal plate 201 and the drillshaft 251 promotes the removal of the drilling dust from the front side209 towards the drilling dust groove 255 during the drilling process.The wedge-shaped intermediate space thereby produces a pump effect whichadditionally propels the drilling dust from the groove 263 into thedrilling dust groove 255 of the drill shaft 251.

FIGS. 4 a and 4 b show another preferred embodiment of the hard metalplate for a rock drill according to the invention, wherein for betterlegibility of the description of the figures, the same referencenumerals as those of the embodiment according to FIGS. 1 a to 1 e, or 2a to 2 f, or 3 a and 3 b, increased by 300 or 200 or 100, are used foridentical and similar components of the hard metal plate.

The hard metal plate 301 differs from the hard metal plates 201 and 101in that the axial section 333 extends over half the axial length of theshort side 305 of the hard metal plate 301. The conical section 337 isachieved by forming a step arrangement 375 having at least three steps,which define three radial jump faces 377 and three axial pedestals 379.The axial pedestal 379 is slightly inclined with respect to the axialdirection A.

The step structure on the conical section 337 facilitates the removal ofdrilling dust from the front side 109 of the hard metal plate 101.

The features disclosed in the preceding description, the figures and theclaims can be important both singly and in any combination forimplementing the invention in the different embodiments.

REFERENCE LIST 1, 101, 201, 301 Hard metal plate 3, 103, 203, 303 Longsides 5, 105, 205, 205 Short sides 7, 107, 207, 307 Bottom side 9, 109,209, 309 Front side 11 to 17, 111 to 117, Cutting flank sections 211 to217, 311 to 317 19, 119, 219, 319 Main cutting edge 21, 121, 221, 321Short cutting edge 25, 125, 225, 325 Edge section near short side 27,127, 227, 327 Edge section remote from short side 31, 131, 231, 331 Tipregion 33, 133, 233, 333 Axial section 35, 135, 235, 335 Transition edge37, 137, 237, 337 Conical section 41, 43, 141 143, Chamfers 241, 243,341, 343 51, 151, 251, 351 Drilling shaft 53, 153, 352, 353 Drillinghead 55, 155, 255 Helical groove 57, 157 257, 357 Slotted flank 161,162, 362 Edge region 163, 263 Drilling dust groove 269 Shoulder 375 Steparrangement 377 Radial jumps 379 Axial pedestal A Axial direction RRadial direction α Angle

1. A rock drill comprising: a hard metal plate inserted into a seatformed at one end of a drill shaft, said drill shaft having a radialdimension defining a first side and a second side of the drill shaft andan axial direction, and said hard metal plate comprising a substantiallyrectangular base shape having two opposed long sides extending in theaxial direction of the drill shaft which are at least partially coveredby the seat, two opposed, substantially axial free short sides, a radialbottom side facing towards the seat and a roof-shaped cutting facefacing away from the seat, wherein both short sides are formed by anaxial section having a purely axial direction component and a conicalsection inclined towards the axial direction, so that at the short side,the substantially rectangular plate tapers towards the bottom sidewherein the hard metal plate protrudes radially beyond both the firstside and the second side of the drill shaft such that a portion of thelong sides are exposed beyond both the first side and the second side ofthe drill shaft.
 2. The rock drill of claim 1, wherein the conicalsection is inclined with respect to the axial direction by less than10°.
 3. The rock drill of claim 1, wherein the conical section formsmore than half of the short sides.
 4. The rock drill of claim 1, whereinthe axial section opens axially linearly into the cutting face and formsless than half of the short sides.
 5. The rock drill of claim 1, whereinthe conical section and the axial section are separated from one anotherby a transition edge.
 6. The rock drill of claim 1, wherein the conicalsection extends linearly in the axial direction from the axial sectiontowards the bottom side.
 7. The rock drill of claim 1 further comprisinga concave groove extending linearly in the axial direction formed on atleast one long side.
 8. The rock drill of claim 7, wherein the grooveextends away from the cutting face and opens along a linear profile intothe bottom side.
 9. The rock drill of claim 7, wherein the groovediminishes radially in the axial direction in the conical section. 10.The rock drill of claim 7, wherein the groove lies at a transition tothe adjacent short side.
 11. The rock drill of claim 1, wherein thecutting face comprises two long cutting edges which meet in a tip regionand each of the two long cutting edges comprise an edge section close tothe tip region and an edge section remote from the tip region, whereinboth the edge section close to the tip region and an edge section remotefrom the tip region are inclined towards a radial directionperpendicular to the axial direction, wherein the edge section close tothe tip region is more strongly inclined than the edge section remotefrom the tip region and a transition region between the edge sectionclose to the tip region and the edge section remote from the tip regionis continuously concavely curved.
 12. The rock drill of claim 11,wherein the edge section remote from the tip region is inclined withrespect to the radial direction by about 5° to 20°.
 13. The rock drillof claim 11, wherein the edge section close to the tip region isinclined with respect to the radial direction by about 25° to 35°. 14.The rock drill of claim 11, wherein the linear edge section remote fromthe tip region is at least five times longer than the linear edgesection close to the tip region.
 15. The rock drill of claim 11, whereinthe cutting face comprises two short cutting edges which extendsubstantially linearly from the long sides into the tip region with thesame inclination towards the radial direction.
 16. The rock drill ofclaim 15, wherein the short cutting edges are inclined with respect tothe radial direction by about 25° to 35°.
 17. The rock drill of claim 1,wherein the cutting face comprises two long cutting edges extendinglinearly radially outwards from a common tip region, which open in alinear course in the respective short side, and are inclined to a flatradial extension of the long sides at an angle greater than 1° and lessthan 10°.
 18. The rock drill of claim 1, wherein the two short sides areformed by a substantially flat side section remote from the bottom sideand a stepped side section close to the bottom side, said stepped sidesection in the conical section comprising at least two steps.
 19. Therock drill of claim 18, wherein the stepped side section comprises aradial jump surface and an axial pedestal surface.
 20. The rock drill ofclaim 19, wherein the pedestal surface is at least twice as large as thejump surface.
 21. The rock drill of claim 19, wherein the pedestalsurface is inclined between 1° and 20° with respect to the axialdirection.
 22. The rock drill of claim 1, wherein the conical section isinclined with respect to the axial direction by about 6°.
 23. The rockdrill of claim 11, wherein the edge section remote from the tip regionis inclined with respect to the radial direction by about 12° to
 13. 24.The rock drill of claim 11, wherein the edge section close to the tipregion is inclined with respect to the radial direction by about 29°.25. The rock drill of claim 15, wherein the short cutting edges areinclined with respect to the radial direction by about 31° to 32°. 26.The rock drill of claim 1, wherein the cutting face comprises two longcutting edges extending linearly radially outwards from a common tipregion, which open in a linear course in the respective short side, andare inclined to a flat radial extension of the long sides at an angle ofabout 5° to 6°.